Method of producing decorative surfaces



Patented Feb. 25, 1936 UNITED STATES PATENT OFFICE METHOD OF PRODUCING DECORATIVE SURFACES Karl Turk, Baltimore, Md., assignor to The Porcelain Enamel 8t Mann! acturing Company of Baltimore, Baltimore, Md., a corporation of Maryland Claims.

The present invention relates to the production of articles carrying a vitreous coating simulating the color, luster and brilliance of a metal.

Polished metals and particularly steel plates 5 and strips have been used for decorative purposes upon, the outside of buildings. In their original state the polished metals possess a brilliance and esthetic appeal, which to a large extent is responsible for their use. However, polished metal surfaces are not resistant to atmospheric influences, including corrosion and oxidation, and therefore after they have been in service for a comparatively short time they discolor and tarnish, thereby losing their original brilliance and esthetic appeal.

While vitreous enamels are characterized by their ability to maintain their luster and color indefinitely, up to the present time they have not been used in the building field for decorative purposes in place of the metals, since it has not been possible to simulate the appearance and finish thereof. For example, it has been impossible to simulate the appearance of silver, gold, aluminum, nickel, chromium and polished stainless steel.

The object of the present invention is to provide an article having a vitreous enameled surface which is resistant to atmospheric influences and simulates the finish and appearance of various metals. While the underlying principles of the present invention are applicable to the production of vitreous enamel finishes simulating that of various metals, it is particularly adapted for the production of articles carrying a transparent vitreous enamel coating, which simulates a gold, silver or silvery finish.

Broadly stated, the invention comprises selecting a metal base having a color component of the metal which it is desired to. simulate and forming thereon a transparent coating of a vitreous enamel having a color component of the metal which it is desired to simulate, the color components combining on firing to produce the finally desired visual appearance of the article. Stated differently, articles carrying vitreous enamel finishes simulating the appearance of metallic surfaces are produced by utilizing the natural color of the base and the color of the vitreous enamel coating. It is quite necessary in order to produce the finishes herein set forth that the enamel be sufliciently transparent or translucent to permit some of the color of the base to which the enamel is applied to show through the enamel. If the enamel has any substantial degree of opacity, internal reflection of the base color is not permitted, and consequently the base 5 color and/or the reaction-product of the base color with the enamel fails to function to assist in imparting to the enamel the desired color and brilliance.

In the preferred form of the invention the 10 enamel which forms the final transparent vitreous coating has added thereto certain color components which act to modify the color components of the base to which the enamel is applied. It has been ascertained that the tone, shade, or 15 brightness of the finish can be controlled by the addition of certain electrolytes. Additionally, it is desirable to add to the enamel certain brilliance-increasing addition agents, all of which will be hereinafter referred to in detail.

In one form of the invention, a metal base having a given color is coated with an enamel frit and the time and temperature of firing is controlled so as to permit what appears to be an absorption of the metal base material by the 5 enamel, thereby producing a third color component different from the color component of the base or the enamel itself. To illustrate, if a copper base has applied thereto an enamel producing a relatively clear enamel of a certain color, on firing there will be a reaction between the base and the enamel, functioning to develop a greenish layer of enamel between the surface enamel layer and the underlying copper base. Very pleasing colors may be obtained with a relatively clear enamel over a copper base, and the firing treatment is such that the reaction between the copper and the enamel is carried on for a sumcient length of time and at the propel-temperature to permit the action and the solution or absorption of a portion of the copper base in the enamel.

In producing vitreous enamel finishes simulating metallic finishes by the method set forth, it has been noted that there appears to be a crystal growth at the contact line between the enamel and the base, and it may be, at least in some instances, that the color, brilliance and appeal of the ultimate finish is in a large measure due to the crystalline growth formed, it is believed, by

' the action of the enamel on themetallic base.

, and firing to produce a transparent or transiucent enamel, there appears to be dispersed throughout the enamel a gold-like crystal. These complexes, or what apparently appears to be crystals, may be copper entrapped in the enamel. or copper compounds produced by reaction between the copper and the enamel, and held in suspension in the transparent or translucent enamel to impart to the vitreous enamel article an appearance simulating gold. The effect of the gold crystals is in greater evidence the, nearer the finish is to a gold finish. Along with these dispersed complexes, which may or may not be in a crystal state, are numerous small bubbles, probably entrapped gas, which cause considerable reflection of light and emphasize the internal reflection, producing a high gloss and metallic appearance. action between the copper base and the enamel appear in their greatest number at the junction of the enamel and the copper base. when the article is examined under the microscope, it appears as if there were a thin coating or layer of a reaction-product or crystals simulating a gold color over the copper base and a transparent coating of enamel over the reaction product. A transparent or translucent green enamel will produce a green colored reaction product immediately adjacent the colored base, and a red enamel will produce red crystals or complexes. The effect of the reaction product is, of course, much less pronounced using colored enamel than when using colorless transparent or translucent enamel.

In order to produce the desired color effect, it is necessary that the enamel coating applied to the metal base not be so thick as to build up so great anopacity as will destroy the desired effect. The thickness of the coating preferably should be that ordinarily used when applying a single coating of enamel to sheet steel, andthis in general is about 36 grams dry weight per square foot for the enamel herein described, and for other enamels the criterion will be as set forthtoo great an opacity shouldnot be built up.

When carrying out the present invention, enamels of various compositions may be used. For example, any of the following batches having coloring addition agents added thereto, may

- be smelted to produce a frit which when mixed with water and a colloidal suspension agent such as bentonite, clay or alginates will produce an enamel which may be applied to the metal base and fired at a temperature of 1525" F. for three minutes:

The above figures represent percentages by weight. It is to be noted that the above enamels .have slight color, this undoubtedly being the composite result of the color of the individual compounds entering into the mixture. Improvement of the gold color can be obtained by adding up to of iron or nickel oxide. As shown in these The complex formed by intersimple enamels, color is sometimes developed. If

it is of such a hue and concentration that it color can be brought about by varying the proportion of the different compounds. It has been ascertained that the final color of the vitreous enamel surface can be controlled to a degree by varying the fusibility and fluidity of the enamel, since for a-given temperature and time of firing the more fusible enamel absorbs more of the base material, with the resultant color change. When using simple mixtures, and these will give satisfactory results, it is desirable to set up the milled enamel. with suitable electrolytes, for example, decinormal HCL. H2804, M8504, to keep the colloidal particles evenly distributed or dis-' persed through the enamel, and thereby prevent them from accumulating in a layer, and blocking the free transmission oflight and destroying the transparencyof the enamel.

The simple mixtures above set forth will, when applied properly on a' base having a copper-surface, develop very good gold colors of relatively high durability. Howe'venfrom the standpoint of economy, smelting practice, and in addition to confer resistance to weathering and mechanical destruction, it is desirable when producing a vitreous enamel finish simulating metallic finishes, to modify the basic formula. Utilizing the basic composition as above set forth, an enamel has been developed which when fired with due care .on a copper surface gives a gold finish, which will indefinitely withstand the attackof weak alkalies and all acids except hydrofluoric acid, and its resistance to impact and deflection will compare very favorably with ordinary high grade porcelain enameled surfaces on iron.

The following mixture has been found exceed-' a 0 ingly satisfactory for producing a gold finishon a base having a copper surface; g

' Parts by weight Silica 59.22 Borax 8.45 Sodium nitrate 6.9

, Cryolite 6.95 Soda ash 10.86 Fluorspar 2.91 Litharge 25.0- Titanium dioxide L 6.5 Potassium phosphate 1.9 Barium carbonate 9.0 Nickel oxide .755 Iron oxide .100 Potassium permanganate I .145

The constituents of the above mix should be of prime commercial quality, carefully weighed and mixed together.v Thereafter the mix is charged into a reverberatory type of smelter and smelted until complete cessation of bubbling occurs. The

,smelted frit may then be tapped into a tankof water and quenched.

Thereafter, the frit is ground in a pebble mill in the presence of water and a colloidal suspending agent such a bentonite, clay or an alginate. For

every 100 pounds of frit there should be added 30 pounds of water, and approximately one-half pound of the colloidal suspending agent such as bentonite, clay and the like. The pebble mill mix is ground to the fineness of about 1% residue on a 150 mesh sieve.

Thereafter the base material, preferably copper, is cleaned to remove any grease or oxide formation, and a medium coat of the above enamel is applied by spraying, dipping, or the like. The water is allowed to evaporate and the enamel is fired onto the copper base at a temperature of 1525 F. for about three minutes. The temperature and time of firing, as above set forth, is satisfactory when the specific enamel referred to is used. Oi course, if the character of the enamel is changed, then it is necessary to modify the time and temperature of firing. However, those skilled in the art will be able to determine the proper firing cycle, including temperature and time, by the following: a series of plates are made up and fired at different temperatures and times. A change of color will be noted passing from red at the lesser firing treatments to green at the greater firing treatments. As the color changes from red to green there is a point where the enamel has the gold appearance. It is to be noted that the composition of the enamel has a substantial effect upon the temperature and time range within which the gold color is developed, and the most desirable composition is that one with which the greatest time and temperature range is obtained. With the composition above set forth, the temperature and time range is quite broad and more than sufficient for practical purposes.

While the gold finish obtained, proceeding in accordance with the above, is fairly satisfactory, the full richness of the gold color may be developed by treating the milled enamel with suitable electrolytes. As previously stated, proper flocculation is necessary to obtain the uniform dispersion of the colloidal particles in the enamel. While all electrolytes exhibit the desired action, some are of particular value. It has been ascertained that the tone of the gold can be to a great extent controlled by the addition to the enamel mix of small amounts of a suitable acid, or mixtures thereof. Hydrochloric acid produces a vitreous enamel having a red-gold finish when the enamel is fired onto a copper surface. Sulphuric acid produces more of a bright gold. While it is not desired to be limited to any particular amount of concentrated acid which is used, it may be stated that satisfactory results are obtained when about 1 c. c. of the acid or mixes thereof are added to one pound of the wet enamel. Changes in the amount of acid used will be suggested to those skilled in the vitreous enameling art.

The brilliance of the gold finish may be enhanced by the addition of suitable salts. For

example, there may be added to the enamel above set forth a small amount of alum, for example A of 1% on the weight of the enamel, and this willincrease the gloss or brilliance of the gold finish considerably. Epsom salts may be used in place of alum. Similar salts may be used to give the same effect, although to a varying degree.

While the composition herein set forth gives the most satisfactory results, variations thereof have been tried and comparable results obtained. These variations will suggest themselves to those skilled in the art. For example, the equivalent of one refractory may be substituted in the composition for another, and as an instance thereof the substitution of alumina for silica is set forth. The fiux used in the composition may be substituted by its equivalents, for example, soda ash for lead oxide. When there is a substitution of one flux for another, or one refractory for another, the proportions thereof can be varied as long as the enamel composition maintains satisfactory fiuidity and working'qualities. For example, in substituting soda ash for lead, the proper amount of soda ash may be added to retain the originad fiuxing power, fluidity and/or softness of the enamel, but since the coeflicient of expansion of sodium oxide (10.0 10") is much higher than that of lead oxide (3.0 10-") and it is desirable that the expansion coefficient of the enamel be not changed, it is expedient that a compensating change in the composition be made by increasing the proportion of some other low expanding component at the expense of one having a higher coefficient of expansion, for instance, the substitution of silica (0.8x10- for alumina (5.0xlor boric oxide (0.1 10") for calcium oxide (5.0x10- or magnesia (0.1 x 10- for calcium oxide.

It is, of course, obvious that if the enamel mix on smelting has too great a fluidity, this can be compensated for by adding a refractory material and the mix will then retain its original characteristics. The point which it is desired to make is that the enamel mix from which the enamel frit is produced can be varied in composition so long as it retains the characteristics necessary for the production of an enamel herein set forth.

It may be stated that the enamel composition must be suitable for proper adhesion to a copper or similar base, have acid resisting properites, and be transparent or translucent. While the enamel may or may not be tinted with suitable coloring agents, the resulting finish upon application to the base should be gold-like in appearance. Its tone and brilliance can be controlled by the addition of suitable electrolytes and salts. The color of the enamel may be controlled by compounds and proportions thereof used in mixing the raw batch, by the electrolyte used for fixing or setting, and by the time and temperature used in firing.

When making a gold finish, in the preferred form of the invention, it is desired to use sheet copper as the base material. However, cast, sprayed or plated copper will work equally as well. The primary requisite is that the surface immediately adjacent to the enamel be a copper surface. Further, while copper is specified, copper bearing alloys or red and yellow metals will equally as well serve as a base material, provided the fusion temperature of the base is sufficient to permit the proper firing of the enamel. Copper or copper alloys of red and yellow metals, simulating the appearance of copper to some extent, and permitting the formation of gold color, may be introduced in the finely divided form into the enamel, and then an iron base or any other base may be used and the desired effect produced, although this method of procedure is not as satisfactory as one using a copper or copper alloy base.

While the invention has been illustrated by the production of a vitreous gold finish simulating the finish that gold is capable of taking, it is, as previously stated, applicable to the production of finishes simulating other metals. For example, a silver finish simulating the finish of silver may be produced by applying the enamel herein disclosed on a nickel However, for the best results when using a nickel base, it is desirable to change the coefilcient of the enamel slightly and thereby obtain better adhesion. Chromium surfaces also have been successfully enameled, and a silvery finish obtained of slightly different hue.

The firing of the base carrying the unfired enamel composition should be carried out in the neutral or a slightly oxidizing atmosphere. l-Iowever, a slightly reducing atmosphere will also give satisfactory results. However, when the atmosphere of the furnace is either oxidizing or reducing to a substantial degree, a proper gold color is difficult to obtain. The following sets forth the results of samples made with the enamel herein disclosed, which. were burned in neutral, reducing and oxidizing atmospheres:

Sample No. g g f Atmosphere Color 7. 5 1575- 90% air-10% Yellowoxygen. green. 15. 157; 90% air-10% Green.

1 ibe t 7. 5: 1575 C Uri-CO..-" Light tan 10. (l 1575 C0|+CO- Tan. 15. 0.; 1575 COg-l-CO.. Brown Under oxidizing conditions the enamel turns green quite quickly. The number of bubbles seem to be greater when prepared under reducing conditions. In reducing atmospheres the crystal condition was quite evident, but it was slightly obscured by the dirty brown color of the enamel. Neutral atmospheres give the best results as far as color and crystal structure are concerned. 1 I

In the claims the expression a base ha'g'ing a copper surface is'intended to include a copper base or a base composed of alloys which will produce a copper color, a yellow color, or a red color, and also bases which are? not made of copper, but which carry a coating feither electroplated or heat plated of copper or alloys thereof, which will produce a surface havifig a color simulating copper or alloys thereof. The expansion factors herein set forth are taken from thermal expansion tables compiled by Winkelmann and Schott.

It is understood that inthe formulas disclosed it is possible to substitute the chemical equivalents for any of the compounds given, in other words, any compound of the element which will combine with ordinary ceramic materials to form a stable frit or glass.

The terms transparent-producing vitreous enamel, transparent vitreous coating and similar terms used in the claims are intended to include any enamel which possesses suillcient transparency to permit such internal reflection of the base color and/or reaction-product of the base color with the enamel as will assist in imparting to the fired enamel the desired visualappearance as to color and brilliance.

What I claim is:

1. The process of producing on a base having a copper surface an article having a gold-like appearing vitreous enamel surface comprising producing an acid resisting vitreous enamel capable of formingon firing an enamel of suflicient transparency to light rays so that the color of the base is visually apparent through the enamel, and containing a metallic oxide selected from the "through the enamel.

group consisting of iron oxide, nickel oxide, and manganese oxide functioning to impart to the enamel a potential color component capable of combining with the copper color component of the base to produce the gold appearance, applying to the base a thin coating of said enamel and firing to produce the gold-like color, the color of the base being visually apparent through they enamel.

2. The process of producing on a base having a copper surface an article hating a gold-like appearing vitreous enamel surface comprising producing an acid resisting vitreous enamel capable of forming on firing an enamel of sufilcient transparency to light rays so that the color of the base is visually apparent through the enamel, and containing a metal bxide selected from the group consisting of iron oxide, nickel oxide and manganese oxide functioning to impart to the enamel a potential color component capable of combining with' the copper color component of the base to produce the gold appearance, and an electrolyte selected from the group consisting of sulphuric acid, nitric acid and hydrochloric acid functioning to control the tone of the gold-like color, anplying to the base a thin coating of said enamel; and firing to develop the gold-like color; the color of the base being visually apparent;

3. The process of producing on a base having; a copper surface an article having a gold-like appearing vitreous enamel surface comprising producing an acid resisting vitreous enamel capable of forming on firing an enamel of 's'jumcient transparency tc light rays so that the fcolor of the base is visually apparent through thefenamel, and containing a metal oxide selected from the group consisting of iron oxide, jnickel oxide and manganese oxide, functioning impart to the. enamel "a potential color component capable of combining with' thecopper color component of' the base, an electrolyte selectedfrom the group consisting of sulphuric acid, nitric acid and hy-,,

drochloric acid functioning to control the tone -of the gold color, and 'an alunfi in a sufilcient,

quantity to increase the brilliance of the final enamel, applying to the base a thin coating of said enamel, and firing to develop the gold-like color, the color get the base being visually apparcut through the enamel.

4. The process of producing on a base having a copper surface an article having a gold-like appearhig vitreous enamel surface comprising producing an acid resisting vitreous enamel con= taining a metal oxide selected from the group consisting of iron oxide, nickel oxide and man= ganese oxide, functioning to impart to the enamei a potential color component capable of combining with the copper color component of the base, said vitreous enamel on firing being of sufilcient transparency to light rays to permit the colcr of the base to be visually apparent through the enamel, an electrolyte selected from the group consist-v ing of sulphuric acid, nitric acid and hydrochloric acid functioning to control the tone of the gold color, and sufficient alum to, increase the brilliance of the final enamel, applying to the base a thin coating of said enamel, and firing to develop the gold-like color, the color of the base being visually apparent through the enamel.

5. The process of producing on a base having a copper surface an article having a gold-like appearing vitreous enamel surface comprising producing an acid resisting vitreous enamel capacombining with the copper color component of the base to produce the gold appearance, applying to the base a thin coating of said enamel, and firing the article in a neutral or slightly oxidizing atmosphere to produce the gold-like color. 5

KARL TURK. 

